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Adds code to keep track of the number of instructions that are
emulated by the in-kernel emulator. Counters for the various classes
of emulated instructions are available under
powerpc/emulated_instructions/ in the root of the debugfs file
system. Optionally (controlled by
powerpc/emulated_instructions/do_warn in debugfs), rate-limited
warnings can be printed to the console when instructions are
emulated.